Of all the culinary superheroes flying into town in the next few weeks -- Ina Garten, Bobby Flay and Jacques Pepin among them -- the one whose cape has the most mileage on it must be Diana Kennedy.

That's not because she has a few years on the lot of them; just how many is a topic the hardy octogenarian does not wish anyone to dwell on. It's because for the past half-century, the expat Englishwoman has crisscrossed Mexico in search of its regional cuisine (or cuisines, as she emphasizes). She has parsed chili peppers, raged against the decline of proper tortillas and dictated techniques to thousands of students in her Mexican and American kitchens.

Eight of her cookbooks have been published in English; the newest is an updated version of 1989's "The Art of Mexican Cooking."

"It is a useful guide," Kennedy says, with heel-raising emphasis on the adjective. "As long as they are still paying attention to me, why not shove what's important right at them?"

Much has been written about her uncompromising approach and untempered assessments. "I'm a terror," she plainly admits. A five-minute audience with her can confirm that, but it also can solidify the impression that she has earned the right to hold forth. Men may defer to her as a learned elder; women often delight in seeing the full potential of a passionate and rigorous life.

To an Anglophile, Kennedy's manner is simply winning, especially when she describes the particulars of her regular afternoon tea.

There must be just-boiled water, whole milk ("none of that blue stuff") and a sweet biscuit. The fresh coffee, fruit and salads that round out her daily diet come from the greenhouse and seven acres that she and a small staff tend in the western state of Michoacan.

Today finds her halfway through her stay in Washington as a guest of José Andrés's ThinkFood Group. In addition to book signings, receptions and a planned appearance at the Mexican Cultural Institute, she will apply some of her remarkable energy and focus to the menu at Oyamel Cocina Mexicana in Penn Quarter, one of Andrés's restaurants.

"I welcome her input," says Oyamel head chef Joe Raffa, a busy and important guy who seemed happy to hold a large reflector panel in place while Kennedy endured a photo session.

When Andrés hired Raffa in late 2006 to head the Oyamel kitchen, Raffa had no experience with Mexican cooking. He left the interview and headed straight to Olsson's bookstore to buy every Diana Kennedy book he could get his hands on, including her first, "The Cuisines of Mexico" (Harper and Row, 1972).

He took his first trip to Mexico in April to take a Kennedy class on tamales. An Oyamel sous-chef soon followed. They both came back and "recooked everything," Raffa says. "We learned this new set of skills. Every time we go, we learn how to do things better."

Kennedy will spend the next two or three days with Raffa's staff, going over . . . what, exactly? Oyamel has earned awards and acclaim for its cuisine.

"There are elements that are not very Mexican," Kennedy announces with gravitas. "The tamales have to be looked at, and the enchiladas. The fillings can be too mushy. We are going to talk about it."

She summarizes the characteristics of not-very-Mexican fare as a matter of over-seasoning -- not that she has accused Oyamel of such offenses: "Too much cumin. Too much onion. Too much garlic." And things need to be cooked down and down to achieve true flavors, she says.

Her visit celebrates her book's return to print and is pegged to the impending Mexican holiday called the Day of the Dead, when family members honor their deceased relatives in a variety of ways, including making special foods. Raffa and Kennedy collaborated to add special fish dishes to the restaurant's menu, including a paella-like rice dish from Veracruz and fish cooked in banana leaves in the style of Mexico's state of Tabasco.

On Saturday, Kennedy demonstrated two easy dishes that also would be served as party food this week. Either could be the heart of a weeknight meal. "Americans reach for pasta when they want to cook something quick," she says. "These are healthful and tasty alternatives."

With the restaurant kitchen already bustling, Raffa found a far corner for Kennedy to work in. Many hands, including Raffa's, were at the ready. She could not pass by workstations without comment:

· A trash bin topped with spent grapefruit halves: "The lack of composting is inexcusable. I hate seeing waste! At my home we compost and recycle everything we can."

· A bubbling pot of green sauce: "The heat's up too high on this. Someone is losing flavor."

· A shiny-smooth stainless-steel griddle: "I'm not keen on what it is doing to the surface of those tostadas."

The two dishes, from Kennedy's "The Essential Cuisines of Mexico" (Clarkson Potter, 2000), benefited from improvisation, even as she touted the importance of following recipes as written.

Calabaza Frita from the Yucatan began not with large chunks of steamed, peel-on calabaza pumpkin but from the vegetable peeled, cubed and sauteed in olive oil to near-tenderness. Habanero chili pepper was used instead of a milder chili dulce.

"Taste and shine. That's what we're going for in this dish," Kennedy said as she added more oil after the tomatoes, green bell pepper and onion had been cooked down. Then the pan was taken off the heat and covered with a piece of (used) aluminum foil Raffa was summoned to fetch. The resting time is critical, she says, for the flavors to meld and for the vegetables to reach the proper texture.

The Camarones en Pipian of Tampico ("that's with an m-A-R-o-n-e-s," spelled for the photographer) created a broth that was used twice in the preparation of the dish. Kennedy boiled the shrimp shells in salted water, then strained the resulting broth and used it to parboil the shrimp and later to help pulverize toasted pumpkin seeds for a sauce.

The sauce would be smoother if the seeds had been ground separately, she said. But because she offered this time-saving method as an alternative in her cookbook, it would suffice here. Assembling and cooking the sauce, then finishing the shrimp in it took less than an hour and produced an elegant, beautiful dish.

With quick cuts of a paring knife, Kennedy created a serrano chili flower, using it and some cilantro to garnish a serving for a close-up shot. To make herself camera-ready, Kennedy dashed a small brush through her new, "unsettled" haircut and applied a dab of coppery lipstick.

"You'd want to chomp on one of these," she said, holding a shrimp by its tail. "You could freeze any leftover broth and add to it as you do other dishes. You could freeze this sauce ahead of time, without the shrimp in it."

Kennedy is known for her way with tamales, too, but those are no quick weeknight affair, as anyone who has made them can attest. The updated "Art of Mexican Cooking" has about eight pages of tips and techniques involving masa, steamers and husks -- and that's before its individual recipes kick in.

She, Raffa and his crew spent much of Monday preparing several hundred tamales for a private party at Oyamel that night. After an initial consult about the optimum texture and taste for Kennedy's Veracruz pork tamales and squash blossom tamales, she and Raffa settled into production mode. Pork lard ("you simply must use it") was whipped until fluffy, then beaten into the masa.

Even with coarsely chopped squash flowers, chili peppers, zucchini, Oaxaca cheese and a small amount of stewed pork blended in with masa for the squash blossom tamales, the filling remained light. "We take a small piece of it and see if it floats in water. That's how we know it's ready," says Raffa. Small, sausage-shaped portions of the mixture were placed in the center of dried corn husks that had been soaked for about 30 minutes.

The float test doesn't work for the Veracruz pork tamale filling, which has a wetter dough. That masa was spread on banana leaves, then two small pieces of chili-stewed pork and some of its sauce went on top. Both tamales were set in the multiple racks of a tamale steamer big enough to hold 150 at a time.

Kennedy had brought her own large, soft hoja santa leaves, an aromatic with anise and peppery overtones that, to her mind, has no acceptable substitute. Small pieces of the leaves went into the pork tamales. (Raffa had the leaves on hand, but Kennedy is not one to leave such things to chance or to use inferior ingredients. She preferred her hoja santa in a side-by-side taste test.)

In that vein, she also brought her own tamale flour, ground by hand. It was coarser, whiter and moister than masa available in the States.

Did she have to sneak it into the country? "I declared what I came here to do," she says. "A nice young woman in Customs started discussing tamales with me, and that was it. I was in."

Les Dames d'Escoffier is hosting a cocktail reception and book signing for Diana Kennedy at Oyamel tonight from 6 to 8. The price is $60 for nonmembers. Call 202-973-2168.